A paddle type and a Savonius type that are known as representative examples of vertical axis drag-type wind turbines directly receives force of a fluid in a holding manner on a wing receiving surface, which is approximately a vertical surface relative to the incoming direction of the fluid, and therefore although the advantage is that movability is good because rotation can be started at a low wind-speed area, and large torque can be produced, it is not possible to attain a rotation speed of a wind turbine equal to or higher than a wind speed and also they are not suitable for converting high energy generated at a high wind-speed area into a rotation energy with high efficiency.
In order to enhance the initial startability of a lift-type wind turbine, which is believed to be poor at startability, a combined water/wind turbine in which a Savonius-type drag-type blade is mounted on the inner rotation side of a Darrieus-type lift-type wind turbine blade have been developed and utilized, wherein the technology is characterized in that the wind turbine has been improved so that rotation is made possible from low fluid-speed areas to high fluid-speed areas.
As a combined water/wind turbine motor, there is also a technology that has improved startability by mounting a drag-type cross flow blade on the inner side of a linear wing surface on the circumferential side and has also improved the rotation efficiency by mounting the cross flow blade in such a manner that a fluid hitting the cross flow blade flows along the blade and effectively hits a lift-type blade.